Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add Casper-Studios/casper-marketplace --skill zod-best-practicesgit clone --depth 1 https://github.com/Casper-Studios/casper-marketplaceWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/casper-studios/casper-marketplace/zod-best-practices)<a href="https://agentmods.dev/skills/casper-studios/casper-marketplace/zod-best-practices"><img src="https://agentmods.dev/badge/skills/casper-studios/casper-marketplace/zod-best-practices/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/casper-studios/casper-marketplace/zod-best-practices"><img src="https://agentmods.dev/badge/skills/casper-studios/casper-marketplace/zod-best-practices.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00038 | $0.00711 |
| Opus 5 | $0.00019 | $0.00356 |
| Sonnet 5 | $0.00008 | $0.00142 |
| Haiku 4.5 | $0.00004 | $0.00071 |
Grade A, and why
zod-best-practices scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 6d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 42 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Zod Best Practices
Treat a Zod schema as the owned contract at an untrusted data boundary: it defines accepted wire values, produces trusted domain values, and makes invalid input an explicit, intentional outcome.
Library Sources
- GitHub repository ID:
colinhacks/zod - Context7 library ID:
/colinhacks/zod - DeepWiki repository ID:
colinhacks/zod
Use Context7 for current documentation and DeepWiki for implementation details.
Effective Strategies for Zod
Read the references that apply to the current task before defining or reviewing Zod schemas and parsing code.
- Make schemas the owned, trusted contract for wire data.
- Keep a schema and its standard string formats as the single source of truth instead of duplicating types or custom format logic.
- Validate serialized data at its trust boundary, including authenticated external payloads, before it becomes a domain value.
- Keep constructors and format validators under one
zimport rather than mixing import forms. - Infer the correct side of a schema with
z.inputorz.inferwhen a transform or default changes accepted input from parsed output instead of hand-writing either type.
- Express the complete protocol contract in the schema.
- Select Zod's top-level validator for a standard string format instead of recreating the format with a custom regular expression.
- Encode missing and
nullwire semantics with the matching wrapper rather than whichever wrapper compiles. - Define defaults with exact domain meaning in the schema; do not use defaults to turn unknown or invalid input into arbitrary fallbacks.
- Dispatch literal-tagged alternatives with
z.discriminatedUnionrather than trying each tagged branch withz.union. - Select the matching object constructor when unknown keys have contract meaning: strip for leniency, reject for closed contracts, or preserve only opaque pass-through data.
- Make validation failure match the boundary and presentation contracts.
- Choose the parse API from the failure contract: abort a violated invariant or return an expected validation branch.
- Derive expected validation presentation from Zod's error instead of discarding its field information.
- Use
.refine()for one value and one boolean rule; move multi-field or multi-issue validation to.check(). - Use
.check()for multi-field relationships with separate actionable issues instead of collapsing them into one.refine()error.
What ships with it
15 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
- agents/openai.yaml 113 B
- LICENSE.txt 16 KB
- references/cross-field-validation.md 1.5 KB
- references/discriminated-unions.md 879 B
- references/object-strictness.md 538 B
- references/parse-failure-contracts.md 689 B
- references/predicate-validation.md 377 B
- references/schema-defaults.md 593 B
- references/schema-input-output.md 469 B
- references/schema-ownership-and-formats.md 554 B
- references/serialized-trust-boundaries.md 667 B
- references/top-level-formats.md 397 B
- references/validation-error-rendering.md 559 B
- references/wire-nullability.md 509 B
- references/zod-imports.md 306 B
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 6d ago Changed · +3 lines · -41 tokens per session cc319f8ad5b8
- 11d ago First seen · 39 lines · 79 tokens per session scan A 3c982dcba721
zod-best-practices is a skill published in the GitHub repository Casper-Studios/casper-marketplace (12 stars, last pushed 6d ago), licensed MPL-2.0. It adds 38 tokens to every session and 711 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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